Rolling bearings, in particular multiple-row angular ball bearings, have to be braced in a directed manner during assembly, in order to ensure a satisfactory running of, for example, the bevel gear of a rear-axle differential. In the series assembly of structural units, for example bevel gear units, of identical type of construction, it has hitherto been customary to determine the respective bearing moment of friction for each structural unit beforehand by applying a defined axial force to the shaft rotating at a defined rotational speed. A collar nut is subsequently attached, mostly at another assembly location. This collar nut is in this case screwed until the bearing moment of friction previously determined for the defined axial force is established once again at the defined shaft rotational speed. This ensures that each structural or gear unit is braced in its rolling bearings with exactly the axial force previously applied.
DE 39 25 388 A1 describes a method for applying a defined pretensioning force to rolling bearings of a shaft, in particular to tapered roller bearings of a bevel wheel shaft of a bevel gear, a collar nut which engages on the shaft and is supported on a stay being screwed in a directed manner, taking into account bearing moments of friction previously determined. The pretensioning force is applied in that, starting from a just brace-free zero point, the collar nut is rotated through a pretensioning angle specific to the type of construction. The pretensioning angle specific to the type of construction must in this case be determined and can subsequently be applied to all structural units of the same type of construction, for example gear units of the same bevel gear.
A three-ring bearing, with at least three rows of rolling bodies and with an intermediate ring arranged between the inner and the outer ring, is known from DE 196 03 701 A1, the intermediate ring being arranged rotatably between two rolling body rows. Moreover, the inner and/or the outer ring likewise has raceways for two rolling body rows and is of split design, the amount of pretension being capable of being set jointly for all three rolling body rows by means of the parting point of the bearing ring. Since the outer system is connected in two ways, to be precise directly via the intermediate ring and indirectly via a rolling body row, the possibility for the different movement of the three rings being maintained, both systems are to be capable of being set by means of one operation, with the result that one rolling body row is to be saved. A rolling bearing of this type with an intermediate ring is suitable only for very special applications and cannot be used on a normal shaft.
DE 100 57 861 A1 discloses a single-row or two-row angular ball bearing for shafts rotating at extremely high speeds, for example of dental drills, which is not to be overloaded by pretensioning during start-up. In the state of rest, with the rotational speed equal to zero, the angular ball bearing is not pretensioned. A pretension is built up on the balls only as a result of rotation and the centrifugal forces at the same time occurring. The arrangement of the balls may take place selectively as a 0-package or as an X-package.
In DE 100 57 861 A1, a pretension controller is provided which varies the pretension as a function of specific operating conditions. The desired pretension is to be established only when the operating rotational speed is reached. In the state of rest, there is axial play, that is to say no pretension is to be set. The absence of pretension makes it possible to run up particularly quickly to the operating rotational speed. This describes, referring to FIG. 2 there, a 0-package consisting of two single-row angular ball bearings with a small axial play in the state of rest.
The axial play is set there in that one end face of the inner ring is machined by cutting in such a way that this end edge is in alignment with the end edge of the outer ring, this being intended to have the effect that the end edges of the inner and the outer ring can be brought into a blocked position with the end faces of the second single-row angular ball bearing. This arrangement is to ensure play, with the result that a tension-free and therefore rapid run-up of the shaft rotating at rotational speeds of above 500 000 rev/min is to become possible. A jamming of the balls between the rings due to the rise of the pretensioning force as a result of the ball centrifugal forces, because of very high rotational speeds, is thereby supposed to be avoided.
U.S. Pat. No. 3,150,471 describes bearing packages which are composed of a plurality of single-row bearings, to be precise of grooved ball bearings or four-point bearings. These are bearings which can absorb axial forces in two directions. The bearings described there have a reversal play in the event of a change in direction of the axial load, and a person skilled in the art can derive from this that the bearings are not pretensioned axially; this is also because the solution described there serves for the uniform force absorption of two or more bearings placed one against the other in tandem. Furthermore, U.S. Pat. No. 3,150,471 describes bearing packages of single-row ball bearings with split inner or outer rings, in which a more uniform load-bearing capacity of the two bearings is to be achieved under load by the projecting dimensions at the parting plane of the split inner or outer ring being ground down. The reason given for this measure is the elimination of the elastic compression which occurs to a differing extent under load from bearing to bearing.
DE 85 01 369 U1 discloses a four-row angular ball bearing with a one-piece outer ring and with a bearing inner ring consisting of two bearing inner ring halves, in which the axially movable bearing inner ring has at each of its outer ends a sliding surface inclined conically outward in the axial direction, a tension ring being arranged between this sliding surface and a radial surface. When a shaft is pushed through, the tension ring is displaced radially along the sliding surface, as a result of which the pretension of the bearing is to be set.
Finally, a power divider for a motor vehicle is known from DE 198 39 481 C2, in which a bevel pinion shaft is mounted in a gear case via two axially pretensioned rolling bearings spaced apart from one another, the rolling bearings being designed as two-row tandem angular ball bearings loadable on one side and set in an O-arrangement with respect to one another. The pretension is generated there in such a way that, by a collar nut being screwed onto the shank of the bevel pinion shaft, the bevel pinion is moved axially in the direction of the case, so that the two bearings are put under pretension. Between the two two-row angular ball bearings, on the shank of the bevel pinion shaft, a spacer sleeve is arranged which is supported, on the one hand, on the inner ring of the bearing and, on the other hand, on a step, not designated, of the shank. When the threaded part is tightened, first, the inner ring is displaced, so that a deformation force is exerted on the spacer sleeve.
Those previously known solutions in which a pretension, that is to say a play-free mounting of the balls between the inner and outer ring, plays a part have in common the fact that the amount of pretension can be set only very inaccurately or in a complicated way. Normally, the pretension is set by measuring the moment of friction or by displacement measurement. Furthermore, in bearings known hitherto, which are used, in particular, for the mounting of bevel pinion shafts, it is comparatively difficult to preassemble these.
The bearing manufacturer usually delivers the components of the bearing in individual parts to the final customer, for example a transmission or automobile manufacturer, who assembles the individual parts, to be precise, mostly, two two-row angular ball bearings with the bearing balls arranged between them, only at the time of mounting on the shaft to be supported. This leads to a considerable amount of time for assembly and, moreover, entails the risk of the loss of individual parts.